Various methods have been described for injecting coilable product, or well string, into a well. One early such design is shown in U.S. Pat. No. 3,559,905 of Palynchuk, issued Feb. 1, 1971, in which a continuous chain with gripping blocks carried by the chain is used to inject the well string into the well. More recently, such continuous chain gripper systems have been described in U.S. Pat. No. 5,553,668 of Council, et al, issued Sep. 10, 1996.
These continuous chain gripper systems have many moving parts which may wear, are complicated and are not readily adaptable to inject parallel well strings. A stepping system has been proposed by Sizer, Canadian patent no. 1,220,418 issued Apr. 14, 1987, but this device used slips to grip the well string, which tend to damage the well string due to the use of teeth and the relatively uncontrollable gripping force exerted by the slips.
Gripper blocks have been used with continuous chain gripper systems that do not damage well string. Gripper blocks have also been used that have optimized stress distribution. Distribution due to the use of plural grooves in the face of the gripping dies, in which successive grooves deepen in the direction of tension.
The inventor has proposed a well string injector in which the gripping advantages of the continuous chain gripper systems are combined with the simplicity and fewer moving parts of the stepper systems.